Species Rhododendrons

By David Tarrant | Image: Judy Newton

Rhododendron yakushimanum

With 800 species, the adaptable rhododendron has made itself at home around the globe, often in rugged and rocky terrain such as the mountains of Asia, where most garden hybrids originate. The species rhododendron differs greatly from its grand, showy cousins with their wonderful blousy blossoms come May. While the latter has been hybridized by human intervention, “species” refers to the original plant just as it occurs in nature.

Species rhododendrons are very diverse, and their many forms are reflective of where they come from. If they are found in high alpine situations like the Himalayas, for instance, they are low growing and mound-shaped in form. In contrast, those that grow in lower-temperate regions are often quite large with flowers similar in form and shape to the showy garden hybrids. This makes sense, of course, since it is the pollen of these low-temperate beauties that has been used to create horticultural hybrids.

I tend to like the species rhodos in that they are uniquely interesting, and always distinctive in their flower form. Also, they tend to bloom earlier in the season, even as early as late January in milder winters such as the one we’ve just experienced.

Like all members of their family, species rhododendrons prefer an acid woodland type of soil that’s rich in humus and well drained, as they are susceptible to Phytophthora, a root-rotting fungal disease.

Rhododendrons are surface rooted, so safeguard these delicate roots by not planting too deeply and by not digging or hoeing among established plants – hand weeding is strongly recommended. Because rhododendrons are associated with woodland settings, gardeners often plant them in deep shade, which is a big mistake. They require good light for at least half a day, and should prosper in a setting such as the east side of a building, or far enough away from a tree so that it casts shade for only half the day, preferably during the hottest hours of 10 am to 3 pm.

Rhododendron moupinense

While there are many wonderful species rhododendrons, I do have my favourites.

Rhododendron moupinense is among the earliest to bloom and is extremely manageable even for the small townhome garden. I’ve even seen it grown successfully in a half barrel on a balcony. At maturity it will reach one metre in height and circumference. The evergreen leaves are small with a few fine hairs at the base of the mid-rib. The white flowers, often flushed pink, are deliciously delicate in appearance and borne in trusses of three to five, resulting in a bloom three to four centimetres wide. The only drawback to R. moupinense is that it blooms so early, often in February, that the flowers are susceptible to frost damage. But don’t let that put you off growing this delightful foreteller of spring.

Rhododendron mucronulatum is another must-have early bloomer. Distinctive in habit and appearance, it is a rather straggling open bush about two metres in height, and is completely deciduous. Very hardy to zone 4, it starts to show colour as early as late January, as was the case this year. The blooms are in trusses of wide-open, bell-shaped pink blossoms about five centimetres in size. A unique feature of R. mucronulatum is that it appreciates open sunny spots – at least this is where one excellent example thrives best in the Winter Garden at UBC.

Rhododendron yakushimanum is another must-have for all gardens, great or small. This evergreen is slow growing, reaching a metre in height and width at maturity, with trusses of flowers that resemble a spectacular dessert. The individual blooms, four to five centimetres across, open with a luscious bright pink that gradually fades to pale pink or white, usually by April. Another enticement of this extraordinary species rhodo is its slightly curled, leathery leaves, which are thickly coated with a furry, cinnamon-brown indumentum that feels like soft ultrasuede. A delightful tactile experience in the garden.